Formulation for Inhibiting Formation of 5-HT2B Agonists and Methods of Using Same

ABSTRACT

Drug combinations and their use are disclosed. A first drug is administered in combination with a second drug. The first drug such as fenfluramine is characterized by the formation of a metabolite including 5-HT2B agonists such as norfenfluramine with known adverse side effects. The second drug is in the form of a CYP inhibitor such as cannabidiol which modulates the formation of metabolite down thereby making the first drug safer.

FIELD OF THE INVENTION

This invention relates generally to the field of pharmaceuticalchemistry and more particular to drug combinations which inhibit theformation of metabolites which act on a 5-HT_(2B) receptor and therebyreduce adverse side effects; and more particularly the combination offenfluramine with drugs that inhibit the formation of norfenfluramine.

BACKGROUND OF THE INVENTION

Drug discovery to identify antiepileptic drugs that are effectiveagainst refractory epilepsies is a formidable challenge. The underlyingetiologies are varied and are poorly understood. Many anti-epilepticdrugs (“AEDs”) are ineffective, or even contraindicated because theyexacerbate symptoms. Often their mechanisms of action can be complex andare often incompletely characterized. Hence it is difficult to predictthe efficacy of new drugs, even those that are structurally related todrugs known to work. A further difficulty is that patients who enroll inclinical trials are often being treated with multiple drugs which, whilenot eliminating seizures, keep them relatively stable. The ability tomodify their treatment is sharply limited, owing to the risk that theircondition will deteriorate and severe, often life-threatening symptomswill recur.

Nonetheless, there have been breakthroughs. An important one isfenfluramine, which is proving highly effective in treating refractoryepilepsies, including Dravet syndrome, Lennox-Gastaut syndrome, Doosesyndrome, and West syndrome. Dravet Syndrome, or severe myoclonicepilepsy in infancy, is a rare and malignant epileptic syndrome. Thistype of epilepsy has an early onset in previously healthy children, andis refractory to most conventional AEDs. Similarly, Lennox-Gastautsyndrome, Doose syndrome, and West syndrome are all severe diseaseswhich are similarly refractory to conventional treatments. Prior tofenfluramine, there were few treatment options for any of thoseconditions which were reliably effective, and none that could eliminateseizures entirely for extended periods.

Fenfluramine, also known as 3-trifluoromethyl-N-ethylamphetamine, is theracemic mixture of two enantiomers, dexfenfluramine andlevofenfluramine. While the mechanism by which it reduces seizures isnot completely understood, fenfluramine increases the level ofserotonin, a neurotransmitter that regulates mood, appetite and otherfunctions. It causes the release of serotonin by disrupting vesicularstorage of the neurotransmitter, and reversing serotonin transporterfunction. It is also known to act directly on 5HT receptors,particularly 5HT1D, 5HT2A, 5HT2C and 5HT7. It does not have significantagonistic effects on the 5HT2B receptor.

Fenfluramine is cleared from the plasma by renal excretion and throughhepatic metabolism into norfenfluramine by cytochrome P450 enzymes inthe liver, primarily CYP1A2, CYP2B6 and CYP2D6, but CYP2C9, CYP2C19 andCYP3A4 also contribute to fenfluramine clearance. See FIG. 7A. Suchmetabolism includes cleavage of an N-ethyl group by CYP450 enzymes toproduce de-ethylated norfenfluramine metabolites such as norfenfluramineas shown below.

Fenfluramine was originally marketed as an anorectic agent under thebrand names Pondimin, Ponderax and Adifax, but was withdrawn from theU.S. market in 1997 after reports of heart valve disease and pulmonaryhypertension, including a condition known as cardiac fibrosis. It wassubsequently withdrawn from other markets around the world. Thedistinctive valvular abnormality seen with fenfluramine is a thickeningof the leaflet and chordae tendineae.

One mechanism used to explain this phenomenon involves heart valveserotonin receptors, which are thought to help regulate growth. 5-HT2Breceptors are plentiful in human cardiac valves. Since fenfluramine andits active metabolite norfenfluramine stimulate serotonin receptors,with norfenfluramine being a particularly potent 5-HT2B agonist, thismay have led to the valvular abnormalities found in patients usingfenfluramine. Supporting this idea is the fact that this valveabnormality has also occurred in patients using other drugs that act on5-HT2B receptors.

More generally, many highly effective drugs are, like fenfluramine,associated with significant risks owing to active metabolites which havetoxic effects. The nature and severity of those risks strongly impact adrug's viability as a therapeutic agent, as well as its marketability,and there are many examples of highly effective drugs that werewithdrawn due to safety concerns.

There is therefore a need in the art for methods of using fenfluramineto treat diseases and conditions responsive to fenfluramine that reducethe patient's exposure to harmful metabolites while maintainingtherapeutically effective levels of fenfluramine. There is also a needin the art for new treatments for refractory pediatric epilepsysyndromes which are safe and effective.

SUMMARY OF THE INVENTION

Provided herein are compositions and methods for reducing exposure of apatient to harmful metabolites of a drug being used to treat thatpatient. For example, the disclosure provides methods and compositionsfor reducing exposure to a drug metabolite with potentially harmfulactivity mediated by a 5-HT_(2B) receptor.

In one aspect, the disclosure provides methods of inhibiting theproduction of harmful metabolites in a subject being treated with a drugthat is metabolized into one or more harmful metabolites, wherein thedrug is coadministered with one or more metabolic inhibitors.

In one embodiment, the drug is fenfluramine or a pharmaceuticallyacceptable salt thereof, and is coadministered with a metabolicinhibitor such as cannabidiol.

In alternate embodiments, the drug, such as fenfluramine, iscoadministered with one or more metabolic inhibitors selected frominhibitors of one or more metabolic enzymes selected from the groupconsisting of CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4.

In alternate embodiments of this aspect, fenfluramine or apharmaceutically acceptable salt thereof is co-administered with one ormore agents selected from the group comprising stiripentol, clobazam andcannabidiol.

In alternate exemplary embodiments, fenfluramine or a pharmaceuticallyacceptable salt thereof is co-administered with stiripentol, or withcannabidiol, or with clobazam.

In alternate exemplary embodiments, the fenfluramine or apharmaceutically acceptable salt thereof is co-administered withcannabidiol and stiripentol, or cannabidiol and clobazam, or stiripentoland clobazam.

In one exemplary embodiment, a fenfluramine active agent isco-administered with all of stiripentol, cannabidiol, and clobazam.

In another aspect, the disclosure provides methods of treating epilepsyor a neurological related disease by co-administering to a subjectfenfluramine or a pharmaceutically acceptable salt thereof incombination with an effective amount of one or more metabolicinhibitors.

In alternate embodiments, the neurological related disease is Dravetsyndrome, or is Lennox Gastaut syndrome, or is Doose syndrome, or isWest syndrome

In another aspect, the disclosure provides methods of suppressingappetite in a subject by coadministering to a subject fenfluramine or apharmaceutically acceptable salt thereof in combination with aneffective amount of one or more metabolic inhibitors.

Pharmaceutical compositions for use in practicing the subject methodsare also provided.

An aspect of the invention in a method of reducing a therapeutic dose offenfluamine, comprising:

administering fenfluamine to a patient; and

administering cannabidiol to the patient,

whereby fenfluamine is administered in an amount which is at least 20%less than a therapeutic dose required when treating the patient for anindication being treated.

The above aspect of the invention includes an embodiment wherein theamount of fenfluramine administered is at least 30% less.

The above aspect of the invention includes an embodiment wherein theamount of fenfluramine administered is at least 40% less.

The above aspect of the invention includes an embodiment wherein theamount of fenfluramine administered is at least 50% less.

The above aspect of the invention includes an embodiment wherein theamount of fenfluramine administered is at least 60% less.

The above aspect of the invention includes an embodiment wherein theamount of fenfluramine administered is at least 70% less.

The above aspect of the invention includes an embodiment wherein theamount of fenfluramine administered is at least 80% less.

The above aspect of the invention includes an embodiment wherein theamount of fenfluramine administered is at least 90% less.

The above aspect of the invention includes an embodiment wherein theindication be treated is appetite suppression.

The above aspect of the invention includes an embodiment wherein theindication be treated is a refractory epilepsy.

The above aspect of the invention includes an embodiment wherein therefractory epilepsy selected is from the group consisting of Dravetsyndrome, Lennox-Gastaut syndrome, and Doose syndrome.

An aspect of the invention is a method of reducing a therapeutic dose ofa first drug, comprising:

administering the first drug to a patient; and

administering a second drug which is a CYP450 enzyme inhibitor to thepatient,

whereby first drug is administered in an amount which is at least 20%less than a therapeutic dose required when treating the patient for anindication being treated.

The above aspect of the invention includes an embodiment wherein theamount of first drug administered is at least 30% less.

The above aspect of the invention includes an embodiment wherein theamount of first drug administered is at least 40% less.

The above aspect of the invention includes an embodiment wherein theamount of first drug administered is at least 50% less.

The above aspect of the invention includes an embodiment wherein theamount of first drug administered is at least 60% less.

The above aspect of the invention includes an embodiment wherein theamount of first drug administered is at least 70% less.

The above aspect of the invention includes an embodiment wherein theamount of first drug administered is at least 80% less.

The above aspect of the invention includes an embodiment wherein theamount of first drug administered is at least 90% less.

The above aspect of the invention includes an embodiment wherein thefirst drug is fenfluramine and the indication be treated is appetitesuppression.

The above aspect of the invention includes an embodiment wherein theCYP450 enzyme inhibitor is cannabidiol and the indication being treatedis a refractory epilepsy.

The above aspect of the invention includes an embodiment wherein therefractory epilepsy selected is from the group consisting of Dravetsyndrome, Lennox-Gastaut syndrome, and Doose syndrome.

These and other objects, advantages, and features of the invention willbecome apparent to those persons skilled in the art upon reading thedetails of treating epilepsy or a neurological condition byco-administering fenfluramine or a pharmaceutically equivalent saltthereof with one or more metabolic inhibitors, as more fully describedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in conjunction with the accompanying drawings. It isemphasized that, according to common practice, the various features ofthe drawings are not to-scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.Included in the drawings are the following figures

FIG. 1 is a flow chart in tabular form detailing assessments and plasmasampling over each of three study periods during the clinical trialdetailed in Example 1.

FIG. 2 consists of two bar charts showing the impact of co-administeringfenfluramine with stiripentol, valproate and clobazam on blood plasmalevels of fenfluramine and norfenfluramine in healthy subjects asdescribed in Example 1.

FIG. 3 is a flow chart diagramming the development of thephysiologically-based pharmacokinetic drug-drug interaction (PBPK DDI)model described in Example 2.

FIG. 4 is a schematic of the physiologically-based pharmacokineticdrug-drug interaction (PBPK DDI) model described in Example 2.

FIGS. 5A to 5E are time-course graphs showing changes in blood plasmalevels of analytes in patients to whom were administered the followingdrugs alone or in combination: fenfluramine (0.8 mg/kg), stiripentol(2500 mg), clobazam (20 mg), or valproic acid (25 mg/kg to a max of 1500mg). FIG. 5A is a time course graph of changes in blood plasmafenfluramine and norfenfluramine in subjects treated with 0.8 mg/kg offenfluramine. FIG. 5B is a time-course graph showing changes in observedblood plasma levels of fenfluramine and norfenfluramine in subjectstreated with 0.8 mg fenfluramine in combination with 3500 mgstiripentol, 20 mg clobazam, and 25 mg/kg (up to max 1500 mg) valproicacid. In both FIGS. 5A and 5B, observed data points from the study inExample 1 are superimposed over curves representing predictedfenfluramine and norfenfluramine exposure levels generated by runningthe PBPK DDI model described in Example 2. FIG. 5C is a time-coursegraph showing changes in observed blood plasma levels of clobazam insubjects given clobazam alone or in combination with fenfluramine. FIG.5D is a time-course graph showing changes in observed blood plasmalevels of stiripentol in subjects given stiripentol alone or incombination with fenfluramine. FIG. 5E is a time-course graph showingchanges in observed blood plasma levels of valproic acid in subjectsgiven valproic acid alone or in combination with fenfluramine. In all ofFIGS. 5C, 5D, and 5E, observed data points from the study in Example 1are superimposed over a curve representing predicted clobazam,stiripentol or valproic acid levels, respectively, generated by the PBPKDDI model described in Example 2.

FIG. 6 compares the observed impact (% change relative to STPNPA/CLBAUC₀₋₇₂) of co-administering fenfluramine with stiripentol, valproicacid, and clobazam on plasma levels of stiripentol, valproic acid, andclobazam with the impact on each drug predicted by the PBPK DDI modeldescribed in Example 2.

FIG. 7 consists of charts 7A, 7B, 7C, 7D, 7E and 7F each of which showsclearance values for specified CYP450 enzymes considering the both renalexcretion and hepatic metabolism, and indicate the relative contributionto overall clearance, based on literature reports and incubation studiesusing human liver microsomes. Clearance values are scaled as follows:blank indicates no contribution, + indicates minimal contribution, and++ indicates partial contribution. Inhibition and induction valuesreflect the relative strength of an agent on enzyme activity, based onliterature reports and data obtained from in vitro study results as wellas the FDA Basic and Mechanistic Static Models, provided by theinventors. Inhibition and Induction values are scaled as follows: blankindicates no effects, 1 indicates weak effects, and 2 indicates strongeffects.

DEFINITIONS

As used herein, the term “subject” refers to a mammal. Exemplary mammalsinclude, but are not limited to, humans, domestic animals (e.g., a dog,cat, or the like), farm animals (e.g., a cow, a sheep, a pig, a horse,or the like) or laboratory animals (e.g., a monkey, a rat, a mouse, arabbit, a guinea pig, or the like). In certain embodiments, the subjectis human.

As used herein, the terms “treatment,” “treating,” and the like, referto obtaining a desired pharmacologic and/or physiologic effect. Theeffect can be prophylactic in terms of completely or partiallypreventing a disease or symptom thereof and/or can be therapeutic interms of a partial or complete cure for a disease and/or adverse effectattributable to the disease. As used herein, the terms “treating,”“treatment,” “therapeutic,” or “therapy” do not necessarily mean totalcure or abolition of the disease or condition, and includes inhibitingthe formation of potentially harmful drug metabolites. Any alleviationof any undesired signs or symptoms of a disease or condition, to anyextent can be considered treatment and/or therapy. Furthermore,treatment can include acts that can worsen the patient's overall feelingof well-being or appearance. “Treatment,” as used herein, covers anytreatment of a disease in a mammal, particularly in a human, andincludes: (a) preventing the disease from occurring in a subject whichcan be predisposed to the disease but has not yet been diagnosed ashaving it; (b) inhibiting the disease, i.e., arresting its development;and (c) relieving the disease, i.e., causing regression of the disease.

As used herein, the term pKa refers to the negative logarithm (p) of theacid dissociation constant (Ka) of an acid, and is equal to the pH valueat which equal concentrations of the acid and its conjugate base formare present in solution.

As used herein, the term “fenfluramine active agent” refers to an agentthat is at least in part a functional equivalent of fenfluramine. Insome cases, the fenfluramine active agent is fenfluramine itself, or apharmaceutically acceptable salt thereof. In some cases, thefenfluramine active agent is a structural derivative of fenfluramine. By“structural derivative” is meant a compound that is derived from asimilar compound by a chemical reaction. In some cases, the fenfluramineactive agent is a structural analog of fenfluramine, i.e., a compoundthat can in theory arise from another compound if one atom or group ofatoms is replaced with another atom or group of atoms, regardless ofwhether that compound has been or could be synthesized using existingmethods. In some cases, the fenfluramine active agent can be astructural analog of fenfluramine wherein one or more atoms are replacedwith isotopes such as deuterium, 15N, and 13C.

As used herein, the term “metabolic enzyme” refers to any enzyme orbiochemical pathway that transforms a molecule into another molecule,whether by chemical modification, conformational changes, ornon-covalent association with another chemical species. The moleculeresulting from the action of a metabolic enzyme is termed a“metabolite.” Many metabolic enzymes and enzyme systems are known in theart, including but not limited to the cytochrome P450 or CYP450 enzymesystem found in the liver, and glucuronosyltransferases found in thecytosol.

As used herein, the term “fenfluramine metabolizing enzyme” refers toany endogenous enzyme that acts on a fenfluramine or fenfluramine analogsubstrate in vivo to produce norfenfluramine or a de-alkylatednorfenfluramine-type metabolite. Any convenient inhibitors of suchmetabolizing enzymes can be utilized in the subject methods andcompositions to block metabolism of the fenfluramine active agent.

As used herein, terms such as “unwanted metabolites,” “undesirablemetabolites,” and the like refer to metabolites that are not desired forany reason. “Harmful metabolites” are metabolites that are associatedwith one or more adverse effects. Illustrative examples of harmfulmetabolites are de-alkylated fenfluramine metabolites such asnorfenfluramine, which activates the 5HT-2B receptor and are associatedwith heart valve hypertrophy. In general, harmful metabolites can actvia any number of pathways and can be associated with any number ofadverse effects.

“Clearance” as used herein refers to the process of removing a moleculefrom the body, and includes but is not limited to biochemical pathwayswhich transform the molecule into its metabolites, and renal clearance.

DETAILED DESCRIPTION OF THE INVENTION

Before the present methods and compositions are described, it is to beunderstood that this invention is not limited to the particular methodsand compositions described, as such can, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present invention will be limited onlyby the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangescan independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, some potential andpreferred methods and materials are now described. All publicationsmentioned herein are incorporated herein by reference to disclose anddescribe the methods and/or materials in connection with which thepublications are cited. It is understood that the present disclosuresupersedes any disclosure of an incorporated publication to the extentthere is a contradiction.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “acompound” includes a plurality of such compounds and reference to “themethod” includes reference to one or more methods and equivalentsthereof known to those skilled in the art, and so forth.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided can be different from theactual publication dates which may need to be independently confirmed.

Overview

The basic concept behind the invention is to provide formulations andmethods of treatment using combinations of certain drugs wherein a firstdrug which has known benefits is metabolized into a metabolite withadverse effects, wherein the first drug is administered with a seconddrug which inhibits metabolism of the first drug into the metabolitewith adverse effects.

The invention is based on the surprising discovery that when certainfirst drugs having metabolites with adverse effects are co-administeredwith certain second drugs, patient exposure to the toxic metabolites arereduced while exposure to the first drug remains within therapeuticlevels. In one exemplary combination, the first drug is a fenfluramineactive agent, and the second drug is cannabidiol. When fenfluramine isadministered in combination with cannabidiol, the formation ofnorfenfluramine is modulated down, while the blood plasma concentrationof fenfluramine is maintained within therapeutic levels. In addition tothe multidrug combination comprising fenfluramine and cannabidiol, otherembodiments are contemplated and are disclosed herein.

An overall purpose of the drug combination is to make it possible totreat patients for a range of different diseases and conditions usingthe first drug while avoiding the adverse side effects of the metaboliteof the first drug. A further purpose is to provide combination therapieswherein the second drug enhances the therapeutic efficacy of the firstdrug. A further purpose is to provide combination therapies wherein thesecond drug provides therapeutic benefits in addition to the therapeuticeffects provided by the first drug.

The methods and multidrug combinations provided by the present inventionand disclosed herein represent improvements over the prior art, in thatthey provide the advantage of improved patient safety as compared tomethods and compositions which employ only the first drug. Further,certain embodiments of the methods and compositions provided by thepresent invention allow for decreased dosing of the first drug whilemaintaining efficacy that is equivalent to the efficacy provided byhigher doses of the first drug when administered as a monotherapy.Further, certain embodiments of the methods and combination provided bythe present invention allow for increased dosing of the first drugwithout increasing the safety risks associated with lower doses of thefirst drug when administered as a monotherapy. Further, certainembodiments of the methods and compositions provided by presentinvention show improved efficacy relative to the methods andcompositions which employ only the first drug. Finally, certainembodiments of the methods and compositions provided by the presentinvention provide therapeutic effects apart from the therapeutic effectsof the first drug.

Multidrug Combinations

Aspects of the invention provided by the present disclosure includemultidrug combinations wherein a first drug which has known therapeuticbenefits and which is metabolized into a metabolite with adverseeffects, is administered with a second drug which inhibits the formationof the metabolite.

Therapeutic agents useful in the multidrug combinations of the presentinvention include fenfluramine active agents, including but not limitedto fenfluramine and pharmaceutically acceptable salts thereof. Othertherapeutic agents, including but not limited to fenfluramine structuralanalogs, are also contemplated.

As discussed above, and without being bound by theory, fenfluramine ismetabolized by cytochrome P450 enzymes, including but not limited toCYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4, intonorfenfluramine. As discussed above, and without being bound by theory,norfenfluramine is a 5HT2B agonist and is likely responsible for theadverse cardiac and pulmonary effects associated with the drug. Thoseeffects can be reduced or eliminated by administering fenfluramine incombination with select second drugs that inhibits metabolism offenfluramine into norfenfluramine, which down-modulates production ofnorfenfluramine. The net result is to increase the ratio offenfluramine:norfenfluramine AUC₀₋₇₂ values in a manner thatsignificantly decreases patient exposure to norfenfluramine whilemaintaining fenfluramine within therapeutic levels. The contributions ofparticular enzymes in overall clearance of those compounds, arepresented in FIGS. 7A and 7B.

Thus, in one aspect the disclosure provides a multidrug combinationwherein a fenfluramine is co-administered with a second drug thatinhibits metabolism of fenfluramine into norfenfluramine by one or moreCYP450 enzyme. In various embodiments, the second drug is an inhibitorof one or more of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, andCYP3A4. In various embodiments, the second drug is an inhibitor ofCYP1A2. In various embodiments, the second drug is an inhibitor ofCYP2B6. In various embodiments, the second drug is an inhibitor ofCYP2C9. In various embodiments, the second drug is an inhibitor ofCYP2C19. In various embodiments, the second drug is an inhibitor ofCYP2D6. In various embodiments, the second drug is an inhibitor ofCYP3A4.

A wide variety of antiepileptic drugs are inhibitors and inducers ofmetabolic pathways. The effects of selected agents are presented inFIGS. 7C to 7F. Stiripentol and clobazam are among the antiepilepticdrugs most often used to treat Dravet syndrome. Stiripentol stronglyinhibits CYP1A2, and CYP3A4, and also inhibits CYP2C9 and CYP2C19,albeit less strongly. See FIG. 7C, based on the European MedicinesAgency European public assessment report review of Stiripentol (firstpublished Jul. 1, 2009) Tran et al., Clin Pharmacol Ther. 1997 November;62(5):490-504, and Moreland et al., Drug Metab Dispos. 1986November-December; 14(6):654-62. Clobazam is a weak inducer of CYP3A4.See FDA Approved Labeling Text for Onfi (clobazam) Tablets for oral use(Oct. 21, 2011). Further, there is evidence that clobazam stronglyinhibits CYP2D6. See FIG. 7D.

Example 1 describes a clinical trial in which drug-drug interactionsbetween fenfluramine and the anti-epileptic drugs stiripentol, clobazam,and valproate were studied in healthy volunteers. The results show thatco-administering fenfluramine with these three drugs reduced patientexposure to norfenfluramine by nearly 30%, while increasing fenfluramineexposure by a factor of 1.67. See FIG. 2. These results demonstrate thatthe patient exposure to norfenfluramine can be significantly reduced byco-administering fenfluramine with metabolic inhibitors whilefenfluramine is maintained within normal range.

Therefore, the present disclosure provides a multidrug combinationwherein fenfluramine is administered with stiripentol, clobazam andvalproate.

Example 2 describes the development and qualification of aphysiologically-based pharmacokinetic (“PBPK”) model for quantifyingdrug-drug interactions between fenfluramine and stiripentol, clobazamand valproate. See FIGS. 3 and 4. Results from model simulations showthat co-administering fenfluramine with stiripentol alone, with clobazamalone, and with both stiripentol and clobazam together, significantlyreduces patient exposure to norfenfluramine. See FIG. 6.

Therefore, the present disclosure provides multidrug combinationswherein fenfluramine is administered with a second drug selected fromstiripentol, clobazam, and the combination of stiripentol and clobazam.In one exemplary embodiment, the multidrug combination comprisesfenfluramine co-administered with stiripentol. In one exemplaryembodiment, the multidrug combination comprises fenfluramineco-administered with clobazam. In one exemplary embodiment, themultidrug combination comprises fenfluramine co-administered withstiripentol and clobazam.

Recently, cannabidiol has been shown to exert inhibitory effects onseveral CYP450 enzymes. It is a potent inhibitor of CYP1A2(time-dependent effect), CYP2B6, and CYP3A4, and has inhibitory effectson CYP2C8, CYP2C9, CYP2C19, and CYP2D6 as well. See FIG. 7F.

Example 3 details the refinement of the PBPK model described in Example2 to provide the capability for simulating the impact ofco-administering fenfluramine with cannabidiol, alone or in combinationwith other drugs, on fenfluramine and norfenfluramine exposure inpatients to whom those drugs are co-administered. The model is qualifiedby comparing the changes in fenfluramine and norfenfluramine exposurepredicted by the model with those observed in healthy volunteers.

Therefore, the present disclosure provides multidrug combinationswherein a first drug which is fenfluramine is co-administered with asecond drug which is cannabidiol.

The multidrug combinations disclosed herein can further include one ormore additional drugs in addition to the first and second drugs. Thethird or more drugs can be a metabolic inhibitor which further inhibitsthe formation of the harmful metabolite from the first drug (therapeuticagent), either by the same or different metabolic enzyme or pathway thanthe second, or an agent that provides further therapeutic benefits,e.g., by enhancing the efficacy of the first drug or providingadditional therapeutic benefits, or an agent that is both a metabolicinhibitor and that provides further therapeutic benefits. Drugs ofinterest in this regard include, but are not limited to acetazolamide,barbexaclone, beclamide, brivaracetam, buproprion, cinacalet, clobazam,clonazepam, clorazepate, diazepam, divaloprex, eslicarbazepine acetate,ethadione, ethotoin, felbamate, gabapentin, lacosamide, lorazepam,mephenytoin, methazolamide, methsuximide, methylphenobarbitol,midazolam, nimetazepam, nitrazepam, oxcarbazepine, paramethadione,perampanel, piracetam, phenacemide, pheneturide, phensuximide,phenytoin, potassium bromide, pregabalin, primidone, retigabine,rufinamide, selectracetam, sodium valproate, stiripentol, sultiame,temazepam, tiagabine, topiramate, trimethadione, valnoctamide,valpromide, vigabatrin, zonisamide, and pharmaceutically acceptablesalts thereof.

Methods

The present disclosure provides methods wherein a first drug which hasknown benefits is metabolized into a metabolite with adverse effects,wherein the first drug is administered with a second drug which inhibitsthe formation of the metabolite. Examples of drugs useful in practicingthe invention are described above.

In one aspect, the present disclosure provides methods of administeringa fenfluramine active agent to a subject in need thereof, e.g., for thetreatment of a host suffering from a disease or condition treatable by afenfluramine active agent (as described in greater detail herein). Afurther aspect of the subject methods is that the fenfluramine activeagent is administered to the subject in combination with a second drugthat inhibits the formation of norfenfluramine.

In one aspect, the multidrug combinations provided herein can be used totreat patients who suffer from or have been diagnosed with a diseases ordisorder, or who experience symptoms for which they are in need oftreatment, such as patients who have been diagnosed with a pediatricepileptic encephalopathies including but not limited to Dravet syndrome,Lennox-Gastaut syndrome, Doose syndrome, and West syndrome, or patientswho experience pediatric refractory seizures, or patients susceptible toSudden Unexpected Death in Epilepsy (SUDEP), or patients diagnosed withAlzheimers disease, and obesity. In one aspect, the multidrugcombinations provided herein can be used to treat, reduce, or amelioratethe frequency and/or severity of symptoms associated with such diseasesor disorders.

By “in combination with” or “in conjunction with”, is meant that anamount of the metabolizing enzyme inhibitor is administered anywherefrom simultaneously to about 1 hour or more, e.g., about 2 hours ormore, about 3 hours or more, about 4 hours or more, about 5 hours ormore, about 6 hours or more, about 7 hours or more, about 8 hours ormore, about 9 hours or more, about 10 hours or more, about 11 hours ormore, or about 12 hours or more, about 13 hours or more, about 14 hoursor more, about 15 hours, about 16 hours or more, about 17 hours or more,about 18 hours or more, about 19 hours or more, about 20 hours or more,about 21 hours or more, about 22 hours or more, about 23 hours or more,about or 24 hours or more, prior to, or after, the fenfluramine activeagent. That is to say, in certain embodiments, the fenfluramine activeagent and metabolizing enzyme inhibitor are administered sequentially,e.g., where the fenfluramine active agent is administered before orafter the metabolizing enzyme inhibitor. In other embodiments, thefenfluramine active agent and metabolizing enzyme inhibitor areadministered simultaneously, e.g., where the fenfluramine active agentand metabolizing enzyme inhibitor are administered at the same time astwo separate formulations, or are combined into a single compositionthat is administered to the subject. Regardless of whether thefenfluramine active agent and metabolizing enzyme inhibitor areadministered sequentially or simultaneously, as illustrated above, orany effective variation thereof, the agents are considered to beadministered together or in combination for purposes of the presentinvention. Routes of administration of the two agents can vary, whererepresentative routes of administration are described in greater detailbelow.

In embodiments of the invention, any metabolizing enzyme inhibiting doseof the metabolizing enzyme inhibitor can be employed. Dosages forspecific metabolic inhibitors are generally within a specified range,but will vary according to the factors which include but are not limitedto the patient's age, weight, CYP2C19 metabolic activity, and thepresence and degree of hepatic impairment. Such a dose is less than thedaily dose of metabolizing enzyme inhibitor that leads to undesirableside effects.

Thus, for cannabidiol, a dose of about 0.5 mg/kg/day to about 25mg/kg/day, such as less than about 0.5 mg/kg/day, about 0.6 mg/kg/day,about 0.7 mg/kg/day, about 0.75 mg/kg/day, about 0.8 mg/kg/day, about0.9 mg/kg/day, about 1 mg/kg/day, about 2 mg/kg/day, about 3 mg/kg/day,about 4 mg/kg/day, about 5 mg/kg/day, about 6 mg/kg/day, about 7mg/kg/day, about 8 mg/kg/day, about 9 mg/kg/day, about 10 mg/kg/day,about 1 mg/kg/day, about 12 mg/kg/day, about 13 mg/kg/day, about 14mg/kg/day, about 15 mg/kg/day, about 16 mg/kg/day, about 17 mg/kg/day,about 18 mg/kg/day, about 19 mg/kg/day, about 20 mg/kg/day, about 21mg/kg/day, about 22 mg/kg/day, about 23 mg/kg/day, about 24 mg/kg/day,to about 25 mg/kg/day, can be employed.

For clobazam, dosing is in accordance with FDA guidelines, with startingdosage, dose titration, and maximum dosage depending on the patient'sbody weight, tolerance, and response. Thus, for clobazam, a dose ofabout 5 mg/day to about 40 mg/day, such as about 5 mg/day, about 7.5mg/day, about 10 mg/day, about 12.5 mg/day, about 15 mg/day, about 17.5mg/day, about 20 mg/day, about 22.5 mg/day, about 25 mg/day, about 27.5mg/day, about 30 mg/day, about 32.5 mg/day, about 35 mg/day, about 37.5mg/day, to about 40 mg/day, can be employed

For stiripentol, dosing is in accordance with FDA guidelines, withstarting dosage, dose titration, and maximum dosage depending on thepatient's body age, tolerance, and response. Thus, for stiripentol, adose of about 20 mg/kg/day to about 50 mg/kg/day, such as about 20mg/kg/day, 21 mg/kg/day, about 22 mg/kg/day, about 23 mg/kg/day, about24 mg/kg/day, about 25 mg/kg/day, about 26 mg/kg/day, about 27mg/kg/day, about 28 mg/kg/day, about 29 mg/kg/day, about 30 mg/kg/day,about 31 mg/kg/day, about 32 mg/kg/day, about 33 mg/kg/day, about 34mg/kg/day, about 35 mg/kg/day, about 36 mg/kg/day, about 37 mg/kg/day,about 38 mg/kg/day, about 39 mg/kg/day, about 40 mg/kg/day, about 41mg/kg/day, about 42 mg/kg/day, about 43 mg/kg/day, about 44 mg/kg/day,about 45 mg/kg/day, about 46 mg/kg/day, about 47 mg/kg/day, about 48mg/kg/day, about 49 mg/kg/day, to about 50 mg/kg/day, can be employed.

As indicated above the dosing amounts of the metabolizing enzymeinhibitor can be based on the weight of the patient or can be preset inamounts that will vary with the inhibitor, for example expressed inmicrogram/day, mg/day or g/day or expressed as a dose administered morefrequently or less frequently. In general, the smallest dose which iseffective at inhibiting metabolism of the fenfluramine active agentshould be used for the patient.

In general, known inhibitors have recommended dosing amounts. Thoserecommended dosing amounts are provided within the most current versionof the Physician's Desk Reference (PDR) orhttp://emedicine.medscape.com/ both of which are incorporated herein byreference specifically with respect to any inhibitors and morespecifically with respect to the dosing amounts recommended for thoseinhibitor drugs.

In connection with the present invention, the inhibitor can be used inthe recommended dosing amount or can be used in a range of from about1/100 to about 100 times, or from about 1/10 to about 10 times, or fromabout ⅕ to about 5 times, or from about ½ to about twice the recommendeddosing amount, or any incremental 1/10 amount in between those ranges.Fenfluramine dosage can in some cases be determined relative to thedosage of the co-therapeutic agent with which it is administered, suchthat the patient's exposure to fenfluramine remains within a therapeuticrange while the dosage of the co-therapeutic agent does not exceedrecommended levels and/or minimizes or prevents unwanted side effectsknown to be associated with the co-therapeutic agent. For example,fenfluramine dosage can be calculated based on a molar or weight ratioof fenfluramine to the co-therapeutic agent. Fenfluramine dosage can beset according to the lowest dose that provides patient exposure withintherapeutic levels when fenfluramine is administered with theco-therapeutic agent. Fenfluramine dosage can be set according to thehighest dosage that provides patient exposure to norfenfluramine thatdoes not exceed limits set by the FDA or which results in an increasedrisk that the patient will experience one or more serious adverseeffects.

In connection with the present invention, fenfluramine can be used inthe dosage amount recommended for fenfluramine administered in theabsence of the co-therapeutic agent, or can be used in a range of fromabout 1/100 to about 100 times, or from about 10 to about 100 times, orfrom about 1/10 to about 10 times, or from about ⅕ to about 5 times, orfrom about ½ to about twice the recommended dosing amount, or anyincremental 1/10 amount in between those ranges.

Stated differently and more specifically, fenfluramine can be used inthe treatment of patients. For example, fenfluramine can be used in thetreatment of patients with a form of epilepsy such as Dravet syndrome,Lennox-Gastaut syndrome, Doose syndrome or other refractory epilepsiesand can also be used in appetite suppression. However, in any contextwhere fenfluramine is used, it can be used in combination with an enzymeinhibitor such as cannabidiol and thereby reduce the dose offenfluramine necessary in order to obtain a therapeutically effectiveresult, and importantly reduce adverse side effects from thefenfluramine.

The therapeutically effective dose of fenfluramine is reduced whencombined with cannabidiol. The reduction in the amount of the fulltherapeutic dose required to obtain a desired therapeutic effect isexpected to be approximately 40%±5%. However, the reduction may be 10%,20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more when the fenfluramine iscombined with cannabidiol (each ±5%).

This discovery that treating patients with the combination offenfluramine and cannabidiol makes it possible to dramatically reducethe dose of fenfluramine, and thereby makes it possible to treat a widerrange of patients with fenfluramine for a wider range of indicationswithout adverse effects. With this particular combination, the inclusionof the cannabidiol makes it possible to reduce the amount ofnorfenfluramine (which is the metabolite of fenfluramine) which thepatient is expose to, thereby reducing side effects.

Pharmaceutical Preparations

Also provided are pharmaceutical preparations. As used herein,pharmaceutical preparations mean compositions that include one or morecompounds (either alone or in the presence of one or more additionalactive agents) present in a pharmaceutically acceptable vehicle. Theterm “pharmaceutically acceptable” means approved by a regulatory agencyof the Federal or a state government or listed in the U.S. Pharmacopeiaor other generally recognized pharmacopeia for use in mammals, such ashumans. The term “vehicle” refers to a diluent, adjuvant, excipient, orcarrier with which a compound of the invention is formulated foradministration to a mammal.

The choice of excipient will be determined in part by the activeingredient, as well as by the particular method used to administer thecomposition. Accordingly, there is a wide variety of suitableformulations of the pharmaceutical composition of the present invention.

In one aspect, the present disclosure provides pharmaceuticalpreparation wherein the active agent is a fenfluramine active agent,i.e., fenfluramine or a pharmaceutically acceptable salt thereof. Thedosage form of a fenfluramine active agent employed in the methods ofthe present invention can be prepared by combining the fenfluramineactive agent with one or more pharmaceutically acceptable diluents,carriers, adjuvants, and the like in a manner known to those skilled inthe art of pharmaceutical formulation. The dosage form of a metabolizingenzyme inhibitor employed in the methods of the present invention can beprepared by combining the enzyme inhibitor with one or morepharmaceutically acceptable diluents, carriers, adjuvants, and the likein a manner known to those skilled in the art of pharmaceuticalformulation. In some cases, the dosage form of the fenfluramine activeagent and the dosage form of a metabolizing enzyme inhibitor arecombined in a single composition.

By way of illustration, the fenfluramine active agent and/or themetabolizing enzyme inhibitor can be admixed with conventionalpharmaceutically acceptable carriers and excipients (i.e., vehicles) andused in the form of aqueous solutions, oils, oil- or liquid-basedemulsions, tablets, capsules, elixirs, suspensions, syrups, wafers,sprinkles, and the like. Such pharmaceutical compositions contain, incertain embodiments, from about 0.1% to about 90% by weight of thefenfluramine active agent and/or the metabolizing enzyme inhibitor, andmore generally from about 1% to about 30% by weight of the fenfluramineactive agent and/or the metabolizing enzyme inhibitor. Thepharmaceutical compositions can contain common carriers and excipientsappropriate to the fenfluramine active agent or to the drugsco-administered with the fenfluramine agent, including carriers suitablefor use with water-soluble drugs, such as corn starch or gelatin,lactose, dextrose, sucrose, microcrystalline cellulose, kaolin,mannitol, dicalcium phosphate, sodium chloride, and alginic acid, andcarriers, and excipients suitable for use with drugs that are poorlymiscible or immiscible in water, such as organic solvents, polymers, andothers. Disintegrators commonly used in the formulations of thisinvention include croscarmellose, microcrystalline cellulose, cornstarch, sodium starch glycolate and alginic acid.

Particular formulations of the multidrug combinations disclosed hereinare in a liquid form. The liquid can be a solution, an emulsion, acolloid, or suspension, such as an oral solution, emulsion, or syrup. Inan exemplary embodiment, the oral solution, emulsion, colloid, or syrupis included in a bottle with a pipette which is graduated in terms ofthe milligram amounts that will be obtained in a given volume ofsolution. The liquid dosage form makes it possible to adjust thesolution for small children which can be administered anywhere from 0.1mL to 50 mL and any amount between in tenth milliliter increments andthus administered in 0.1, 0.2, 0.3, 0.4 mL, etc.

A liquid composition will generally consist of a suspension, suspensionor solution of the fenfluramine active agent and/or the metabolizingenzyme inhibitor or pharmaceutically acceptable salt in a suitableliquid carrier(s), for example, ethanol, glycerine, sorbitol,non-aqueous solvent such as polyethylene glycol, oils or water, with asuspending agent, preservative, surfactant, wetting agent, flavoring orcoloring agent. Alternatively, a liquid formulation can be prepared froma reconstitutable powder.

Particular formulations of the invention are in a solid form.

Particular formulations of the invention are in the form of atransdermal patch.

EXAMPLES

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how tomake and use the present invention, and are not intended to limit thescope of what the inventors regard as their invention, nor are theyintended to represent that the experiments below are all or the onlyexperiments performed. Efforts have been made to ensure accuracy withrespect to numbers used (e.g. amounts, temperature, etc.) but someexperimental errors and deviations should be accounted for. Unlessindicated otherwise, parts are parts by weight, molecular weight isweight average molecular weight, temperature is in degrees Centigrade,and pressure is at or near atmospheric.

Example 1 Drug-Drug Interaction Study: Effects of Co-AdministeringFenfluramine with Stiripentol, Clobazam and Valproate on Plasma Levelsof Fenfluramine and Norfenfluramine

The effects of co-administration of a three-drug regimen on fenfluraminemetabolism and resultant plasma levels of fenfluramine and itsmetabolite norfenfluramine was assessed in a clinical trial using inhealthy volunteers. Interim results are reported below.

A. Trial Objectives and Design

A randomized, open-label, single-dose, 3-way cross-over study wasdesigned to examine the effects of co-administering fenfluramine with athree-drug cocktail consisting of stiripentol, clobazam, and valproate.Each patient was treated sequentially with three treatment regimens,each being administered individually, according to six differenttreatment sequences which were assigned randomly.

Regimen B (stiripentol Agent Dose Regimen A regimen) Regimen CFenfluramine 0.8 mg/kg X X Stiripentol 3,500 mg X X Clobazam 20 mg X XValproate 25 mg/kg X X (≤1,500 mg)

Treatment Sequence Period 1 Period 2 Period 3 1 A B C 2 B C A 3 C A B 4C B A 5 A C B 6 B A C

B. Selection of Subjects

Subjects were recruited from an existing pool of volunteers or throughdirect advertising, Prospects who had participated in a study withinthree months prior of dosing were excluded from the pool of potentialparticipants. A full medical history for the preceding 12-month periodwas obtained from each subject's primary care physician and evaluated.Patients were then assessed according to the inclusion and exclusioncriteria shown below. Persons chosen as study participants underwent ascreening visit prior to participation to reassess and confirmcompliance with those criteria.

1. Inclusion Criteria

1. Healthy males.

2. Non-pregnant, non-lactating healthy females.

3. Age 18 to 50 years of age, inclusive.

4. Body mass index within the range of 19.0 to 31.0 kg/mg2 and a minimumweight of 50.0 kg, inclusive, at screening, or if outside the range,considered not clinically significant by the investigator.

5. Are medically healthy with no clinically significant condition thatwould, in the opinion of the investigator, preclude study participation,such as significant, renal endocrine, cardiac, psychiatric,gastrointestinal, pulmonary or metabolic disorders. Subjects should haveno hepatic dysfunction.

6. Have no clinically significant abnormalities in their clinicallaboratory profile that would, in the opinion of the investigator,preclude study participation, including liver function tests outside ofthe normal range.

7. Are non-smokers for at least 3 months (this includes e-cigarettes andnicotine replacement products) and test negative (<10 ppm) on a breathcarbon monoxide test at screening and admission

8. Must agree to use an adequate method of contraception.

9. Female subjects of non-childbearing potential must be surgicallysterile (e.g., tubal occlusion, hysterectomy, bilateral salpingectomy,as determined by subject medical history) or congenitally sterile, or atleast 2 years post-menopause. Females of childbearing potential must useappropriate contraception.

10. Able to speak, read, and understand English sufficiently to allowcompletion of all study assessments.

11. Subjects must voluntarily provide written informed consent.

12. Subjects, in the Investigator's opinion, must be able to completestudy procedures.

13. Must be willing to comply with the requirements and restrictions ofthe study.

Inclusion criteria 2 and 7 from the list above are re-assessed atadmission/pre-dose.

2. Exclusion Criteria

1. Women of childbearing potential who are pregnant or breastfeeding.

2. Male subjects with pregnant partners

3. Have uncontrolled blood pressure (BP), i.e., subject has a supinesystolic BP>160 mmHg or <90 mmHg, and/or a supine diastolic BP>100 mmHgor <40 mmHg at screening or admission.

4. Have an oxygen saturation <92% on room air.

5. Have hypersensitivity or idiosyncratic reaction to fenfluramine,stiripentol, clobazam or valproic acid.

C. Assessments

An overview of study procedures is provided in the trial flow charttable presented in FIG. 1.

D. Results

Interim results of the drug-drug (DDI) study are shown in FIG. 2.AUC₀₋₇₂ values were calculated based on blood plasma levels offenfluramine and norfenfluramine levels. Exposure impact is expressed asa ratio of AUC₀₋₇₂ values determined for patients receiving thecombination treatment to the AUC₀₋₇₂ values determined for patientsreceiving fenfluramine alone. Those results show an increase in patientexposure to fenfluramine by a factor of 1.66 and a decrease innorfenfluramine exposure by a factor of 0.59 when fenfluramine isco-administered with a combination of stiripentol, clobazam, andvalproic acid.

Example 2 Development & Qualification of a Physiologically-BasedPharmacokinetic (“PBPK”) Model for Predicting Drug-Drug Interactions

A physiologically-based pharmacokinetic (PBPK) model able to quantifypotential drug-drug interactions (DDI) and facilitate dose justificationfor clinical trials of fenfluramine (FEN) was developed, qualified, andthen used to predict the impact of co-administering one or moreanti-epileptic drugs (AED), specifically stiripentol (STP), valproicacid (VPA) and clobazam (CLB).

A. Model Development

See FIGS. 3 and 4. The PBPK models for the concomitant medications weredeveloped by refining published PBPK models from the literature; themodel for fenfluramine was developed de novo using basic properties ofthe molecule (fraction unbound, pKa, etc.). Drug interactions wereaccounted for by adjusting the simulated metabolic enzyme efficienciesat each simulated time point according to the concomitant medicationconcentration in the liver at that time point. PBPK models accounted forage-dependent factors such as blood flow, tissue volume, glomerularfiltration rate, CYP maturation, hepatic intrinsic clearance, andbioavailability. Each model was comprised of ten perfusion-limitedtissues.

Tissue-to-plasma coefficients for FEN and its metabolite norfenfluramine(norFEN) were calculated by integrating physiochemical and in vitroproperties such as Log P, pKa, and fup; See Xenobiotica (2013) 43:839).FEN was eliminated by renal excretion and hepatic metabolism; 76% ofhepatic intrinsic clearance (CL_(int)) was converted into norFEN. SeeArch Int Pharmacodyn Ther, (1982) 258:15, and J Pharmacy Pharmacol(1967) 19:49S.

The STP PBPK model was developed by the refinement of a published PBPKmodel, in which STP was eliminated solely via liver metabolism. SeePharm Res (2015) 32:144. Refinement involved the incorporation of asecondary elimination route of renal clearance into the system. Both theCLB and the VPA PBPK models were developed by refinement of previouslypublished models. See Pharm Res (2015) 32:144 and Eur J Pharm Sci (2014)63:45.

For the drug-drug interaction, the inhibitory effects of stiripentol andclobazam on FEN elimination were described by reversibly inhibitingCYP1A2, CYP3A4, CYP2C9, CYP2C19, and CYP2D6-mediated hepatic metabolismbased on the liver concentrations of the concomitant medications. Modeldevelopment was conducted in Berkeley Madonna (v 8.3.18).

The hepatic intrinsic clearance of FEN in combination (CL_(int, DDI))can be calculated as

${\frac{{CLint},_{DDI}}{CLint} = {\frac{{fm},_{{CYP}\; 1\; A\; 2}}{1 + \frac{C_{{STP},{liv}}}{K_{I,{1\; A\; 2}}}} + \frac{{fm},_{{CYP}\; 2D\; 6}}{1 + \frac{C_{{CLB},{liv}}}{K_{I,{2\; D\; 6}}}} + \frac{{fm},_{other}}{1 + \frac{C_{{STP},{liv}}}{{Ki},_{other}}} + {fm}}},_{{CYP}\; 2\; B\; 6}$

Where fm,_(other) includes fm,_(CYP3A) and fm,_(CYP2C19)

B. Model Qualification

The model was qualified by comparing the changes in fenfluramine andnorfenfluramine exposure observed in the study described in Example 1above with the effects predicted by the model. FIGS. 5A through 5E showthat predicted changes in blood plasma levels of fenfluramine,norfenfluramine, stiripentol, clobazam and valproic acid are in closeagreement with the changes observed in healthy volunteers, therebydemonstrating the model's robustness.

C. Predicted Effects of Co-Administering Fenfluramine with One or Bothof Clobazam and Stiripentol on Blood Plasma Levels of Fenfluramine andNorfenfluramine

The PBPK DDI model was used to predict the impact of co-administeringfenfluramine with one or both of stiripentol and clobazam. Results arepresented in FIG. 6.

Example 3 Extrapolation and Refinement of the PBPK Model to IncludeCannabidiol Effects on Fenfluramine Exposure

The model developed as described in Example 2 is further refined toprovide the capability to simulate the impact of co-administering FENwith cannabidiol (CBD), alone or in combination with other drugs, onfenfluramine and norfenfluramine exposure. In particular, the modeldescribed in Example 2 is amended to account for cannabidiol'sinhibitory effects on metabolic enzymes that metabolize fenfluramine,i.e. CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4, and thetime-dependency of CBD's inhibitory effects on CYP1A2.

Example 4 Extrapolation and Refinement of the PBPK Model to IncludeCannabidiol Effects on Fenfluramine Exposure

The effects of co-administration of a two-drug regimen comprisingfenfluramine and cannabidiol on fenfluramine metabolism and resultantplasma levels of fenfluramine and its metabolite norfenfluramine isassessed in a clinical trial using healthy volunteers according to theprotocol described in Example 1, with the exception that stiripentol andclobazam are replaced with cannabidiol, administered at a dose of 10mg/day and 25 mg/day, respectively. Patients receiving fenfluramine aredosed at either 0.2 mg/kg/day or 0.8 mg/kg/day.

The preceding merely illustrates the principles of the invention. Itwill be appreciated that those skilled in the art will be able to devisevarious arrangements which, although not explicitly described or shownherein, embody the principles of the invention and are included withinits spirit and scope. Furthermore, all examples and conditional languagerecited herein are principally intended to aid the reader inunderstanding the principles of the invention and the conceptscontributed by the inventors to furthering the art, and are to beconstrued as being without limitation to such specifically recitedexamples and conditions. Moreover, all statements herein recitingprinciples, aspects, and embodiments of the invention as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope of the presentinvention, therefore, is not intended to be limited to the exemplaryembodiments shown and described herein. Rather, the scope and spirit ofpresent invention is embodied by the appended claims.

1.-20. (canceled)
 21. A method of reducing or ameliorating seizures in apatient, comprising: administering a therapeutically affective amount ofliquid formulation of fenfluramine or a pharmaceutically acceptable saltthereof; and administering a therapeutically affective amount ofstiripentol thereby modulating down formation of norfenfluramine andresulting in higher levels of fenfluramine.
 22. The method of claim 21,wherein the patient is diagnosed with Dravet syndrome.
 23. The method ofclaim 21, wherein the patient is diagnosed with a form of refractoryepilepsy selected from the group consisting of Dravet syndrome,Lennox-Gastaut syndrome, Doose syndrome, and West syndrome.
 24. Themethod of claim 21, further comprising: co-administering to the subjectan effective amount of a co-therapeutic agent selected from the groupconsisting of acetazolamide, barbexaclone, beclamide, brivaracetam,buproprion, cannabidiol, cinacalet, clobazam, clonazepam, clorazepate,diazepam, divaloprex, eslicarbazepine acetate, ethadione, ethotoin,felbamate, gabapentin, lacosamide, lorazepam, mephenytoin,methazolamide, methsuximide, methylphenobarbitol, midazolam,nimetazepam, nitrazepam, oxcarbazepine, paramethadione, perampanel,piracetam, phenacemide, pheneturide, phensuximide, phenytoin, potassiumbromide, pregabalin, primidone, retigabine, rufinamide, selectracetam,sodium valproate, sultiame, temazepam, tiagabine, topiramate,trimethadione, valnoctamide, valpromide, vigabatrin, zonisamide, andpharmaceutically acceptable salts thereof.
 25. The method of claim 24,wherein the patient is diagnosed with a form of refractory epilepsyselected from the group consisting of Dravet syndrome, Lennox-Gastautsyndrome, Doose syndrome, and West syndrome.
 26. The method of claim 21,further comprising: co-administering to the subject an effective amountof a co-therapeutic agent selected from the group consisting ofclobazam, and valproate.
 27. A method of reducing or amelioratingseizures in a patient diagnosed with a form of refractory epilepsyselected from the group consisting of Dravet syndrome, Lennox-Gastautsyndrome, Doose syndrome, and West syndrome, comprising: administering aliquid formulation of fenfluramine or a pharmaceutically acceptable saltthereof to the patient in an amount in the range of 0.2 mg/kg/day to 0.8mg/kg/day; and administering a therapeutically affective amount ofstiripentol in a liquid formulation in an amount of about 20 mg/kg/dayto about 50 mg/kg/day thereby modulating down formation ofnorfenfluramine and resulting in higher levels of fenfluramine.
 28. Themethod of claim 27, wherein the patient is diagnosed with Dravetsyndrome
 29. A method of reducing or ameliorating seizures patientdiagnosed with Dravet syndrome, comprising: administering atherapeutically affective amount of liquid formulation of fenfluramineor a pharmaceutically acceptable salt thereof to the patient in anamount in the range of 0.2 mg/kg/day to 0.8 mg/kg/day; and administeringa therapeutically affective amount of a liquid formulation stiripentolin an amount of about 20 mg/kg/day to about 50 mg/kg/day therebymodulating down formation of norfenfluramine and resulting in higherlevels of fenfluramine.